An electrical fire at Toronto's landmark CN Tower was extinguished Wednesday morning after firefighters took turns climbing into an antenna mast to deal with smouldering wiring and insulation.

The fire broke out around 4 a.m. around an electric cable in the tower's main antenna mast, Toronto Fire said. The section is about 480 metres above the ground — just above the tower's Skypod observation deck.

Some 30 firefighters and seven fire trucks were at the scene.

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Fortunately, they didn't have to take the stairs.

"We took the elevator up," Toronto Fire District Chief Stephan Powell said. "We had to go up to the Skypod level, took a second elevator to get there. And then we had to climb about (30 metres) up an access ladder to reach the affected conduit."

Firefighters could only climb the ladder one at a time to get at the fire, Powell said. Other firefighters "staged" equipment at the base of the ladder so it could be hauled up and used easily.

Firefighters are used to working at heights, Powell said, but the tight space was a challenge to navigate.

"We were dealing with what appeared to be an electrical issue in a very confined space," he said.

Traditional hoses weren't used as spreading water on an electrical fire is quite dangerous, Powell explained. Instead, firefighters hauled up carbon dioxide and dry chemical extinguishers to deal with the fire.

In anticipation of the cramped space, Powell said firefighters also hooked up their respirator masks to tubes connected to an air supply, instead of carrying portable air cylinders.

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The CN Tower shut off power to its antenna during the operation, he added, which affected some local TV and radio signals.

Fighting the fire wasn't all that dissimilar to handling several underground hydro vault explosions in downtown Toronto over the past few months, Powell said.

"What we ended up doing here was — over a thousand feet up — pretty much the same thing," he said.

The fire itself wasn't a roaring blaze. Powell described it as "tar-like", and said insulation on the electrical cable, as well as the wiring, was melting.

The electrical fire was put out just before 7:15 a.m., and Powell said it isn't clear at this point what caused it.

The CN Tower announced on its official Twitter page Wednesday morning that it was open to the public as usual.

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Neil Jones, chief operating officer for the tower, said the fire had posed no threat to public safety or the structure. He said all cleaning staff present at the time were cleared from the building and no injuries were reported.

The CN Tower, a concrete communications and observation tower in downtown Toronto, is more than 550 metres high. It held the record for the world's tallest free-standing structure until 2007.

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